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Improve comment in get_partition_dispatch_recurse.

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David Rowley, reviewed by Amit Langote, and revised a bit by me.

Discussion: http://postgr.es/m/CAKJS1f9yyimYyFzbHM4EwE+tkj4jvrHqSH0H4S4Kbas=UFpc9Q@mail.gmail.com
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Robert Haas 2018-05-16 10:46:55 -04:00
parent 6bd1b4c31b
commit 09b12d52db
1 changed files with 8 additions and 14 deletions
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22
src/backend/executor/execPartition.c
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@ -970,20 +970,14 @@ get_partition_dispatch_recurse(Relation rel, Relation parent,
* partitions are processed as well and a corresponding PartitionDispatch
* object gets added to *pds.
*
* About the values in pd->indexes: for a leaf partition, it contains the
* leaf partition's position in the global list *leaf_part_oids minus 1,
* whereas for a partitioned table partition, it contains the partition's
* position in the global list *pds multiplied by -1. The latter is
* multiplied by -1 to distinguish partitioned tables from leaf partitions
* when going through the values in pd->indexes. So, for example, when
* using it during tuple-routing, encountering a value >= 0 means we found
* a leaf partition. It is immediately returned as the index in the array
* of ResultRelInfos of all the leaf partitions, using which we insert the
* tuple into that leaf partition. A negative value means we found a
* partitioned table. The value multiplied by -1 is returned as the index
* in the array of PartitionDispatch objects of all partitioned tables in
* the tree. This value is used to continue the search in the next level
* of the partition tree.
* The 'indexes' array is used when searching for a partition matching a
* given tuple. The actual value we store here depends on whether the
* array element belongs to a leaf partition or a subpartitioned table.
* For leaf partitions we store the 0-based index into *leaf_part_oids,
* and for sub-partitioned tables we store a negative version of the
* 1-based index into the *pds list. When searching, if we see a negative
* value, the search must continue in the corresponding sub-partition;
* otherwise, we've identified the correct partition.
*/
pd->indexes = (int *) palloc(partdesc->nparts * sizeof(int));
for (i = 0; i < partdesc->nparts; i++)